A ratchet tensioner, also sometimes referred to as a “ratchet-type tensioner,” is used for suppressing vibration generated during the travel of an endless, flexible transmission medium, such as a timing belt or timing chain, which transmits rotation from the crankshaft to a camshaft of an engine, and for maintaining proper tension in the transmission medium. The tensioner mechanism typically includes a tensioner lever pivotally supported on the engine. A plunger, protruding from a housing of the tensioner, presses the back of the pivoted tensioner lever, near an end thereof remote from its pivot axis, thereby holding a shoe surface of the tensioner lever in sliding contact with the slack or return side of the transmission medium to impart tension.
A conventional ratchet type tensioner 31, as shown in FIGS. 8 to 12, includes a plunger 33 provided in a housing 32. The plunger protrudes retractably from a front surface of the housing, being biased in the protruding direction by a plunger spring 36. A ratchet pawl 34, pivotally supported in the housing 32 on a shaft 34A, is biased by a spring 38, as disclosed in Japanese Patent No. 3226037 (see page 2, FIGS. 5 to 10).
In the ratchet type tensioner 31, retraction of the plunger 33 is blocked by the engagement of pawl teeth 34B, formed on the pawl 34, with ratchet teeth 33B, formed on a side surface of the plunger 33.
The tensioner 31 includes an external plate 37 fixed to an end of a shaft 34A, which protrudes outside the housing 32. The shaft is also fixed to the ratchet pawl 34. When the tensioner 31 is shipped, or is being mounted on an engine block, a stop pin 39, as shown in FIG. 10, is inserted into a pin-insertion hole 37A in the plate 37, and at the same time the stop pin 39 is in abutting relationship with an outer wall surface 32A at an end of the housing 32, or alternatively the stop pin 39 may engage a stop hole 32B formed in a side wall of the housing as shown in FIGS. 11 and 12. In both cases, the pawl teeth 34B are maintained in engagement with the ratchet teeth 33B of the plunger 33, so that the plunger is held against protruding movement. After the tensioner is mounted on an engine block, the stop pin 39 may be released so that the tensioner 31 can operate normally.
To produce the conventional ratchet type tensioner 31, it was necessary to connect the external plate 37 to the shaft 34A, and, in the case of the embodiment shown in FIGS. 11 and 12, it was also necessary to drill a hole 32B for insertion of the stop pin 39 into the housing 32. These steps resulted in increased production costs.
Another problem arose where there was a only a small clearance between the tensioner housing 32 and adjacent parts of the engine block. In this case, mounting of the tensioner on the engine block, and the mounting and demounting of a chain, could not be performed easily because of interference between the stop pin 39 and the engine block.
Accordingly, the objects of the invention are to solve the above described problems encountered in the manufacture and installation of conventional ratchet-type tensioners; to provide a plunger stop for a ratchet type tensioner which can be more easily mounted of the tensioner on an engine block; to provide for easy mounting and demounting of the chain; and to reduce the difficulty and cost of production of the tensioner.